Claudin-5 regulates mitochondrial bioenergetics and protects the heart against myocardial infarction.

Claudin-5 (Cldn5) is traditionally recognized as a key component of endothelial tight junctions, however, its potential intracellular function within cardiomyocytes remains largely unexplored. This study aims to explore the molecular mechanisms underlying the cardioprotective role of Cldn5 on myocardial infarction (MI). We identified mitochondrial localization of Cldn5 in cardiomyocytes in human heart tissues and cardiomyocytes by western blot, histochemistry, immunofluorescence and immuno‑gold electron microscopy. Knockdown of Cldn5 in HL-1 cells via siRNA decreased mitochondrial number, increased cellular ADP/ATP ratio, accelerated the accumulation of mitochondrial reactive oxygen species (ROS) and downregulated the signal pathways governing energy metabolism and mitochondrial biogenesis while Cldn5 reversed these metabolic defects. Besides, knockdown of Cldn5 in the mouse left ventricular myocardium via shRNA adeno-associated virus (AAV) led to arrhythmia, myocardial atrophy, cardiac fibrosis and increased mortality. Proteomic analysis revealed that Cldn5 knockdown resulted in 43 differential expressed proteins (DEPs) that disrupt key metabolic pathways. Furthermore, we observed downregulated Cldn5 in the left ventricular myocardium after myocardial infarction (MI). AAV-mediated overexpression of Cldn5 significantly protected the heart against ischemic injury by reducing infarct size, preserving mitochondrial number, decreasing ADP/ATP ratio and mitochondrial ROS production, and enhancing the signal of energy metabolism and mitochondrial biogenesis. Mechanistically, we show that Cldn5 regulates the AMPK/ACC energy sensing pathway and the PGC-1α/NRF1/TFAM mitochondrial biogenesis axis. These findings unveil a non-canonical role for Cldn5 as a crucial regulator of mitochondrial bioenergetics and suggest that targeting Cldn5 may offer a novel therapeutic strategy for ischemic heart disease.